Tree nuts such as cashews can be dangerous to the many people who are allergic to them. Improved processing methods might help reduce the allergenicity of cashews, according to research presented yesterday in the Division of Agricultural and Food Chemistry at the American Chemical Society national meeting in San Francisco.

The main allergens in cashews are proteins called Ana o 1, Ana o 2, and Ana o 3. Previous work has shown that some of these allergenic proteins are sensitive to strong reducing agents.

Now, Christopher P. Mattison and coworkers show that when two of these allergenic proteins are treated with the mild reducing agent sodium sulfite, the antibodies that trigger the allergic reaction are less likely to recognize them. Sodium sulfite is approved for use in food processing and is “generally recognized as safe” by the Food & Drug Administration. The researchers treated aqueous extracts of ground raw and roasted cashews with 50 mM sodium sulfite at temperatures ranging from 0 °C to 100 °C (J. Agric. Food Chem. 2014, DOI: 10.1021/jf501117p).

The researchers tested the treated extracts on serum samples from people who are allergic to cashews. They observed a reduction in antibody binding to Ana o 2 and Ana o 3 in treated extracts. They saw the largest effect with the extract that had been heated the most.

“The sulfite is thought to reduce disulfide bonds in allergens and alter their structure,” Mattison, a researcher at the U.S. Department of Agriculture’s Agricultural Research Service in New Orleans, told C&EN. “Some of the cashew allergens are dependent upon disulfide bonds for proper folding, and sulfite acts to disrupt this connection. This makes it harder for them to be seen by IgE, the type of antibody that causes the reaction.”

Being able to use an approved agent such as sodium sulfite to reduce allergenicity “has significant appeal,” said Kenneth H. Roux, a biology professor at Florida State University who studies food allergens. However, he noted, the sulfite concentration used to treat the aqueous extract was relatively high; still higher concentrations would probably be needed “to treat more complex foods” such as whole nuts, he suggested. “Even if successful, sulfite treatment could significantly alter or negatively affect food quality.”

Mattison and coworkers already have under way further studies with whole cashews. “We will also need to assess safety, nutritional, and sensory aspects of the treated nuts,” he said. “The goal is to process nuts so that they are unable to cause allergic reactions, but if we can reduce or eliminate the number of life-threatening severe reactions, that would be a great step forward.”